1. Field of the Invention
This invention relates in general to voice coil actuators and, in particular, to an improved coil construction and construction method which reduces vibration in the coil of the voice coil actuator.
2. Description of the Prior Art
Disk files are used extensively in data processing systems to store data on a rotating magnetic disk at a particular address. The disk generally has a plurality of concentric recording tracks which are numbered so that the address of the data involves at least a track number and sometimes a disk number where the file includes more than one disk or recording surface. The data address is supplied to a transducer positioning system which has the function of positioning a magnetic transducer to the center of the addressed track.
In order to increase data storage capacity of the disk surface, the center-to-center spacing between adjacent disk tracks has been decreased to the point where track densities currently are in the range of 800 to 1000 tracks per inch. At these densities, the transducer positioning system must, of necessity, be of the track following type in order to maintain the transducer centered on the track throughout the entire revolution of the disk. Track following servo positioning systems operate by sensing a prerecorded servo pattern which has been placed on another surface or interleaved with data on the track. The sensing of the servo pattern is achieved by either a separate servo transducer which is moved conjointly with the data heads or, in some systems, by the data head itself. Variations of the servo head from the center of the track are converted to position error signals that are supplied to the voice coil actuator and function to correct the position error and move the heads back over the center of the track.
It will, therefore, be appreciated by persons skilled in the art that since the servo transducer is moved by the coil of the VCM, it is important to insure that spurious movement of the head relative to the servo pattern does not occur, especially where the spurious movements are cyclic and at a frequency which is outside the range of frequency correctable by the servo system. Considerable effort is, therefore, taken to insure that the components of the system are designed to avoid vibrations, particularly those frequencies which correspond to natural resonances that might occur as the coil is energized by the position error signals during the track following situation and during the track positioning operation.
Analysis of the dynamic performance of positioning systems employed in current commercial disk files indicates that a major source of vibration in the file is the coil of the VCM. The coil assembly must, of necessity, be rigidly attached to the head arms and to the movable carriage in order to obtain positioning accuracy and repeatability.
The coil assembly generally has a tendency to vibrate and resonate in a longitudinal direction parallel to the coil axis when energized. Various arrangements have been suggested in the prior art to minimize this tendency. See, for example, U.S. Pat. No. 4,144,466 assigned to the assignee of the present invention and the prior art referenced in that patent.
In order to increase the track density and obtain even greater storage capacity of the data in the disk, it is desirable and often times necessary to further decrease the amplitude of longitudinal resonance vibrations in the actuator upon energization of the coil. In the past, this has generally required a complete redesign of the various mechanical components of the positioning system along with considerable modelling and testing to minimize vibration problems.
The present invention is directed to a coil construction and construction method which does not require a redesign of the basic mechanical hardware of the system in order to achieve a reduction in longitudinal vibration resonances in the actuator.